The Avogadro Constant for the Definition and Realization of the Mole

Abstract

The International System of Units' (SI) base unit of the quantity "amount of substance" is the mole (symbol: mol). After the revision of the SI to be implemented in 2019, when all SI units will be based solely on constants, the mole will be defined through a fixed value of the Avogadro constant N A . One mole contains exactly 6.02214076 × 10 23 elementary entities, meaning the mole will no longer be linked to the kilogram. Currently, the mole is defined via the mass of exactly 0.012 kg of the 12 C isotope which links it to the kilogram prototype. The history, changes, and implications of the revised definition of the mole are discussed here from the chemist's point of view. The ability to count entities such as atoms or molecules (precisely enough to enable a revision of the SI and preserve consistency of previous and future measurements) is crucial. This is achieved with the realization (Mise en Pratique) based on the X-ray-crystal density (XRCD) method (counting the atoms in a silicon sphere). The determination of N A , focusing on the measurement of the molar mass of silicon highly enriched in the 28 Si isotope, with the lowest uncertainty so far, is presented.

A systematic study of Galactic infrared bubbles along the Galactic plane with AKARI and Herschel. II. Spatial distributions of dust components around the bubbles

“…N37 and S7 have large βc in the white square regions where the bridge features have been observed. Such high βc values have been observed in dense cold molecular clouds (e.g., Kuan et al 1996;Lis & Menten 1998;Planck Collaboration et al 2011), and dust grains coated with thick icy mantles can have βc significantly higher than 2 (e.g., Aannestad 1975;Güttler 1952;Wickramasinghe 1967). Therefore, this result suggests that CCC may increase βc due to the presence of cold dense clouds which are likely to be formed on the collision surface.…”

Wie viele Moleküle enthält ein Mol?

“…Nach der bisherigen Definition der Einheit Mol erfolgt die Rückführung für den (theoretischen) Fall eines Reinstoffs über eine Wägung und den Bezug zur molaren Masse der Substanz. Die molare Masse eines Stoffes ist das Produkt aus der Summe der durchschnittlichen relativen Atommassen aller beteiligten Elemente eines Moleküls entsprechend ihrer stöchiometrischen Zusammensetzung und der Molaren Massekonstante M u .…”

“…In everyday life, there are no direct consequences for the end user; clinical laboratory results or environmental measurements can still be used. [15].…”

New Eras in Physics

“…[1] With this, the French metrology institution BIPM will give up its traditional role as host of the famous "Grand K", the kilogram prototype, which is to be replaced by a fixed value of the Planck constant h. [2] At the same time, also the elementary charge e, [3] the Boltzmann constant k, [4] and the Avogadro constant N A [5] received new definitions so that in the future all seven SI units will be defined in terms of physical constants. [1] With this, the French metrology institution BIPM will give up its traditional role as host of the famous "Grand K", the kilogram prototype, which is to be replaced by a fixed value of the Planck constant h. [2] At the same time, also the elementary charge e, [3] the Boltzmann constant k, [4] and the Avogadro constant N A [5] received new definitions so that in the future all seven SI units will be defined in terms of physical constants.…”

“…On 16 November 2018, the 26th meeting of the General Conference on Weights and Measures in Versailles adopted a resolution on the revision of the International System of Units (SI). [1] With this, the French metrology institution BIPM will give up its traditional role as host of the famous "Grand K", the kilogram prototype, which is to be replaced by a fixed value of the Planck constant h. [2] At the same time, also the elementary charge e, [3] the Boltzmann constant k, [4] and the Avogadro constant N A [5] received new definitions so that in the future all seven SI units will be defined in terms of physical constants. These changes will come into effect on 20 May 2019, and on this occasion Annalen der Physik will publish a special issue "The Revised SI: Fundamental Constants, Basic Physics and Units", edited by our Editorial Advisory Board member Klaus Blaum (Max Planck Institute for Nuclear Physics Heidelberg), Dmitry Budker (Johannes Gutenberg University of Mainz), Andrey Surzhykov (Technical University and Physikalisch-Technische Bundesanstalt -PTB, Braunschweig), and Joachim H. Ullrich (President of the PTB, the National Metrology Institute of Germany) (Figure 1).…”